Electrochemical cell having venting current collector and seal assembly

ABSTRACT

A low profile collector and seal assembly for sealing the open end of a container of an electrochemical cell and providing venting of pressurized gases. An electrochemical cell has a can with a closed bottom end and an open top end, positive and negative electrodes disposed in the can, and a collector and seal assembly disposed in the open top end of the can for closing the open top end of the can. The collector and seal assembly includes a current collector and an annular seal that move relative to each other from a sealed position to a vented position when the internal cell pressure reaches a pressure threshold to vent pressurized gases.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/034,687, filed Dec. 20, 2001, entitled Electrochemical Cell HavingVenting Current Collector and Seal Assembly, currently pending, which isincorporated herein by this reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to electrochemical cells (i.e.,batteries) and, more particularly, to a current collector and sealassembly for sealing the open end of a cell container and providingpressure relief for venting gases when exposed to excessive pressure.

Conventional alkaline electrochemical cells generally include a steelcylindrical can having a positive electrode, referred to as the cathode,which commonly comprises manganese dioxide as the active material. Theelectrochemical cell also includes a negative electrode, referred to asthe anode, which commonly comprises zinc powder as the active material.In bobbin-type cells, the cathode is typically formed against theinterior surface of the steel can, while the anode is generallycentrally disposed in the can. A separator is located between the anodeand the cathode, and an alkaline electrolyte solution simultaneouslycontacts the anode, the cathode, and the separator. A conductive currentcollector is inserted into the anode active material to provide anelectrical path to a negative outer terminal. An annular polymeric(e.g., nylon) seal provides closure to the open end of the steel can toseal the active electrochemical materials in the sealed volume of thecan. An inner cover radially supports the seal. The current collector,inner cover, and seal are typically assembled together to form acollector and seal assembly.

Cylindrical alkaline cells are typically sealed closed by placing thecollector and seal assembly in the open end of the steel can andcrimping the upper end of the can inwardly and over the outer peripheryof the seal to compress the seal. However, electrochemical cellscommonly employ electrochemically active materials, such as zinc, whichgenerate hydrogen gas, particularly when subjected to abusive dischargeconditions, such as battery reversal, as well as during storage, andsometimes during or following service use. When the can is sealedclosed, excessive build-up of high pressure gases within the sealed canmay force the crimped closure open and cause damage to the cell and/orthe device in which the cell is employed.

One approach to avoiding a potentially excessive build-up of pressure ina cell has been to employ a resealable valve system that periodicallyreleases excessive pressurized gases from within the active cell volume.However, the continued periodic release of pressurized gases may, insome situations, permit the release of electrolyte solution containingsalts or other particulate matter, which may foul the resealable valve,and such systems generally require additional costly components. Anotherapproach to avoiding excessive build-up of internal pressure involvesemploying a sealed membrane that is intended to blow out when exposed toexcessive pressure either by puncture or rupture of the membrane itself.A puncture mechanism, such as a spiked member, may be employed to puncha hole in the sealed membrane once the internal pressure reaches apredetermined amount.

A further approach to venting excessively pressurized gases has includedthe use of a vent formed in the seal which is intended to rupture uponexperiencing an excessive pressure build-up in the sealed intervalvolume of the cell. As an example, U.S. Pat. No. 5,667,912 discloses acurrent collector assembly having a seal with a thinned portion formedin the seal diaphragm axisymmetrical about a rotation of the centrallongitudinal axis of the cell. The thinned portion of the seal isintended to shear when the internal pressure exceeds a predeterminedpressure threshold, to thereby create a pressure relief vent passage.

While the aforementioned conventional approaches have served to venthigh pressure gases in commercial cells, many of these approachesinvolve complex seal designs which consume a significant amount ofvolume. Increased collector and seal assembly volume generally resultsin reduced internal volume available for electrochemically activematerials, thus limiting the service performance capability of the cell.Additionally, some conventional venting seals exhibit poor leakageperformance. Further, the venting pressure is generally limited inconventional rupture type venting seals due to the difficulty ininjection molding the thinned portion of the seal. Accordingly, it istherefore desirable to provide for an electrochemical cell having asimplified, low profile collector and seal assembly that effectivelyvents pressurized gases at a predetermined pressure, is capable ofachieving lower vent pressures, and exhibits enhanced leakageperformance.

SUMMARY OF THE INVENTION

The present invention improves the protective safeguards of anelectrochemical cell with an easy-to-manufacture and low profilecollector and seal assembly for sealing the open end of anelectrochemical cell container and providing controlled venting ofpressurized gases. To achieve this and other advantages, and inaccordance with the purpose of the invention as embodied and describedherein, the present invention provides for an electrochemical cellhaving a container with a bottom end and an open top end, and positiveand negative electrodes and an electrolyte disposed in the container.The cell further includes a collector and seal assembly disposed in theopen top end of the container for closing the open top end of thecontainer. The collector and seal assembly includes a current collectordisposed in contact with one of the positive and negative electrodes,and a seal member having an opening defined by an upstanding wall. Thecurrent collector is interference fit within the opening in the sealmember such that the seal member is in sealing engagement with a shaftof the current collector. The current collector and the upstanding wallof the seal member are axially (i.e., parallel to a longitudinal axis ofthe cell) moveable relative to each other upon experiencing apredetermined pressure to move from a sealed position to a vent positionso as to provide a pressure relief passage to vent pressurized gases.

According to one aspect of the invention, the current collector has ashaft extending through an opening defined by an upstanding wall in acentral hub of the seal member, and the current collector moves withinthe opening from a sealed position to a vent position to provide apressure relief passage. According to another aspect of the invention,the current collector has a shaft extending through a central openingdefined by an upstanding wall in the seal member and sealingly engagedwith the upstanding wall of the seal member forming the central opening,and the central hub of the seal member moves on the shaft from a sealedposition to a vent position to provide a pressure relief passage.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims and appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cutaway view of an electrochemical cell having a collectorand seal assembly according to a first embodiment of the presentinvention, shown in a sealed (non-vented) position;

FIG. 2 is a cutaway view of the electrochemical cell of FIG. 1 with thecollector and seal assembly shown in a vented position;

FIG. 3 is a partial cutaway view of an electrochemical cell having acollector and seal assembly according to a second embodiment of thepresent invention, shown in a sealed (non-vented) position;

FIG. 4 is a partial cutaway view of the electrochemical cell of FIG. 3with the collector and seal assembly shown in a vented position;

FIG. 5 is a partial cutaway view of an electrochemical cell having acollector and seal assembly according to a third embodiment of thepresent invention, shown in a sealed (non-vented) position;

FIG. 6 is a partial cutaway view of the electrochemical cell of FIG. 5with the collector and seal assembly shown in a vented position;

FIG. 7 is an elevated perspective view of the collector connector shownin the embodiment of FIG. 5;

FIG. 8 is a partial cutaway view of an electrochemical cell having acollector and seal assembly according to a fourth embodiment of thepresent invention, shown in a sealed (non-vented) position;

FIG. 9 is a partial cutaway view of the electrochemical cell of FIG. 8with the collector and seal assembly shown in a vented position;

FIG. 10 is a partial cutaway view of the electrochemical cell of FIG. 8with the collector and seal assembly partially retracted from the ventedposition;

FIG. 11 is an elevated perspective view of the annular seal member shownin the embodiment of FIG. 8;

FIG. 12 is a partial cutaway view of an electrochemical cell having acollector and seal assembly according to a fifth embodiment of thepresent invention, shown in a sealed (non-vented) position; and

FIG. 13 is a partial cutaway view of the electrochemical cell of FIG. 12with the collector and seal assembly shown in a vented position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a cylindrical alkaline electrochemical cell 10 isshown having a collector and seal assembly 30 according to a firstembodiment of the present invention. Electrochemical cell 10 includes acylindrical steel can 12 having a closed bottom end 14, an open top end16, and a cylindrical side wall extending between the bottom and topends. The closed bottom end 14 of can 12 has a positive cover welded orotherwise attached thereto and formed of plated steel, with a protrudingnubbin 18 at its center region, which forms the positive contactterminal of cell 10. Assembled to the open top end 16 of steel can 12 isthe collector and seal assembly 30, and an outer negative cover 50,preferably formed of plated steel, which forms the negative contactterminal of cell 10. A metalized, plastic film label 20 is formed aboutthe exterior surface of steel can 12, except for the ends of steel can12. Film label 20 is formed over the peripheral edge of the positivecover and may extend partially over the peripheral edge of the negativecover 50.

A positive electrode 22, also referred to herein as the cathode, isformed about the interior surface of steel can 12. According to oneexample, the cathode 22 is formed of a mixture of manganese dioxide,graphite, potassium hydroxide solution, and additives. A separator 24,which is preferably formed of a non-woven fabric that prevents migrationof any solid particles in the cell, is disposed about the interiorsurface of cathode 22. A negative electrode 26, also referred to hereinas the anode 26, is disposed with an electrolyte inside the separator 24and in contact with a current collector 32. The electrolyte may includean alkaline electrolyte containing potassium hydroxide (KOH). Accordingto one example, the anode 26 is formed of zinc powder, a gelling agent,and additives. The manganese dioxide and zinc employed in the cathode 22and anode 26, respectively, are electrochemically active materials.Accordingly, the cathode 22 is configured as the cell's positiveelectrode, and the anode 26 is configured as the cell's negativeelectrode.

The current collector 32 contacts the outer negative cover 50 whichforms. the negative contact terminal of cell 10. The current collector32 is generally configured in the shape of a nail having an elongatedcylindrical shaft 34, a truncated conical tip 35 at the lower end, andan enlarged head 36 at the upper end. The elongated shaft 34 is disposedin contact with the anode 26 and, in this embodiment, has asubstantially uniform diameter. The current collector 32 is connected tothe outer negative terminal 50 via a coiled conductive connector 38 thatis compressible. The coiled connector 38 may be welded to the bottomsurface of outer negative cover 50 and/or to the upper surface ofenlarged head 36 of current collector 32, or alternately may be held incontact therewith via pressure contact. Current collector 32 andconnector 38 serve as an electrical current path to provide the negativepolarity at the outer negative cover 50.

An annular polymeric seal 40 is disposed in the open end of steel can 12to prevent leakage of electrochemically active cell materials containedin steel can 12. Polymeric seal 40 may comprise a syntheticthermoplastic resin such as nylon. Alternate materials for seal 40 mayinclude polypropylene, such as Noryl® Extend which is commerciallyavailable from General Electric Company, and other materials that wouldbe recognized as suitable for seal 40.

Seal 40 has a central hub 42 with an inner upstanding cylindrical wall44 defining a central opening (i.e., aperture) for receiving the currentcollector 32. Hub 42 is generally defined as the central portion of seal40 containing upstanding wall 44 which is compressed against the currentcollector 32. The enlarged head 36 of current collector 32 is generallyoversized for the hub opening, and thus the seal 40 is compressedagainst the current collector 32 to form an interference fit engagementwith the inner upstanding wall 44 defining the hub opening. Theupstanding wall 44 of central hub 42 is configured to sealingly engagethe enlarged head 36 of current collector 32 when in a sealed(non-vented) position. The central hub 42 also has an upper edge 43shown in FIG. 1 formed over the upper peripheral surface of enlargedhead 36 to further resist upward movement of current collector 32. Aninner cover 46, which is preferably formed of a rigid metal, is providedto increase the rigidity and support the radial compression of annularseal 40, thereby improving the sealing effectiveness. The inner cover 46is configured to contact an outer upstanding wall of central hub 42 andan upstanding wall at the outer peripheral section 45 of seal 40. Whilean oversized current collector 32 and an inner cover 46 are used tocompress the seal 40 against the current collector 32, other compressiontechniques such as compression rings may be employed to provide a sealedinterference fit engagement between the current collector 32 and seal40. The seal 40, inner cover 46, and outer negative cover 50 provide alow profile closure to the open end 16 of can 12. In addition, the outernegative cover 50 also includes one or more vent openings 52 that serveto expose the non-sealed volume of cell 10 to the surrounding outsideatmosphere. Vent openings 52 serve to vent pressure build-up releasedfrom within the cell 10 to the outside atmosphere once the collector andseal assembly 30 vents.

Together, the current collector 32, annular seal 40, and inner cover 46form the collector and seal assembly 30 which may be assembled togetherand inserted as a unit into the open end 16 of steel can 12. Theassembly of the collector and seal assembly 30 and closure of the openend 16 of can 12 include disposing the annular polymeric seal 40 in theopen end 16 of the can 12, which may have a flared opening or a beadformed radially inward on the inner wall of the can 12, and crimping theupper end of the can 12 inwardly and over the outer periphery 45 of theseal 40 to compress the seal 40 against the inner cover 46. It shouldalso be appreciated that the outer negative cover 50 is electricallyinsulated from the steel can 12 by way of annular polymeric seal 40.

According to the present invention, the current collector and sealassembly 30 seals closed the open end 16 of can 12, provides anelectrical current path to the outer negative terminal 50, and furtheracts a pressure relief mechanism when exposed to an excessive pressuredifferential. The collector and seal assembly 30 is designed to releasepressurized gases from within the sealed active volume of cell 10 whenthe assembly 30 is exposed to a predetermined pressure differential. Thepressure differential is the difference between the internal pressurebelow the seal 40 and the atmospheric pressure above the seal 40. Thepressurized gas venting is generally achieved by relative axial (i.e.,parallel to a longitudinal axis of the current collector 32) movementbetween the current collector 32 and annular polymeric seal 40. Thepressurized gases released from the internal volume exit cell 10 viaopenings 52 provided in the outer negative cover 50.

According to the first embodiment, current collector 32 is interferencefit and sealingly engaged with annular seal 40 while in the sealed(non-vented) position as shown in FIG. 1. The sealing engagement isformed between the head 36 of collector 32 and the upstanding wallforming hub 42 of seal 40. As the pressure increases within the sealedvolume, which is generally below the bottom surface of seal 40, such asmay occur during an abusive condition, the internal pressure applies aforce on the current collector 32 which will tend to urge the currentcollector 32 upward and out of sealing engagement with annular seal 40.When the pressure differential of the internal sealed volume, ascompared to the outer atmospheric pressure, exceeds a predeterminedpressure threshold, the current collector 32 is forced free from thesealing engagement with the hub 42 of seal 40 and moves to a ventedposition as shown in FIG. 2. The forced disengagement causes the upperfolded end 43 of hub 42 to bend upward to allow upward movement ofcollector head 36. When this occurs, the current collector 32 is forcedupward relative to the entire hub 42 of seal 40 which remainssubstantially fixed in place. It should be appreciated that the hub 42of seal 40 generally will not move upward more than a small distancecompared to the movement of the current collector 32, and thus isconsidered substantially fixed. In the vented position, a pressurerelief passage 48 is provided between the seal hub 42 and the currentcollector 32 to allow for the release of pressurized gases from withinthe internal volume of cell 10. In addition, when the current collector32 moves from the sealed position to the vented position, the coiledconductive connector 38 is compressed between the top surface of thecurrent collector head 36 and the bottom surface of outer negativeterminal 50. When compressed, coiled conductive connector 38 may applyan opposing spring bias force downward such that when the pressuredifferential decreases to a reduced pressure threshold, the currentcollector 32 may be biased downward so that the collector head 36sealingly engages the seal hub 42. In the event that the internalpressure increases after resealing, the current collector 32 will againbe forced upward to open the pressure relief passage 48 to further ventpressurized gases.

An electrochemical cell 10′ is shown in FIGS. 3 and 4 having analternatively configured current collector 32′ as part of a collectorand seal assembly 30′. The current collector 32′ includes a main shaft34 that extends to the uppermost end, without the enlarged head portionas discussed above. Instead, current collector 32′ includes a pluralityof longitudinal flutes (i.e., channels) 62 extending upward toward theuppermost end. It is preferred that the inner upstanding wall formingthe hub of seal 40 be no higher than the length of the flutes 62. Thecurrent collector 32′ is positioned in the sealed position such that theplurality of flutes 62 are located below seal 40, as shown in FIG. 3.The current collector 32′ is interference fit and sealingly engaged withthe inner upstanding wall forming the opening in hub 42 of seal 40.During the venting operation, the current collector 32′ is forced upwardrelative to the entire hub 42 of seal 40 which remains substantiallyfixed in place as discussed above. When a sufficient internal pressureforces the current collector 32′ upward, the longitudinal flutes 62provide a pressure relief passage around the inner upstanding wallforming the hub of seal 40 as shown in FIG. 4. While a plurality offlutes 62 is shown, it should be appreciated that any one or more flutesmay be employed according to this embodiment.

Referring to FIGS. 5-7, an electrochemical cell 10″, according to athird embodiment, is shown similar to cell 10 of FIG. 1, except havingan alternatively configured conductive connector 38′ for providing anelectrical current path between the current collector 32 and outernegative cover 50. Conductive connector 38′ is shown in FIG. 7 generallyconfigured as a bowl-shaped disk made of conductive material, such assteel. With particular reference to FIG. 5, the upper outer peripheralrim engages the bottom surface of outer negative cover 50, while thebottom dome contacts the upper surface of current collector head 36.Conductive connector 38′ preferably provides a downward biased force tothe current collector 32 so as to maintain a sealed engagement with theannular seal 40 while in the sealed (non-vented) position. When thesealed internal pressure reaches a predetermined pressure, relative tothe atmospheric pressure, the current collector 32 moves to a ventedposition, as shown in FIG. 6, during which the conductive connector 38′compresses vertically to allow formation of the pressure relief passage48. Once the internal pressure decreases to a lower pressure, theconductive connector 38′ may force the current collector 32 back intosealing engagement with seal 40, as discussed above in connection withthe first embodiment.

An electrochemical cell 110 is shown in FIGS. 8-10 having a collectorand seal assembly 130 according to a fourth embodiment of the presentinvention. Electrochemical cell 110 includes a steel can 12, label 20,cathode 22, separator 24, and an anode 26, as described above inconnection with the first and second embodiments. According to thefourth embodiment, electrochemical cell 110 includes collector and sealassembly 130 for sealing closed the open end 16 of can 12, providing anelectrical current path to an outer negative cover 150, and providing apressure relief mechanism to vent pressurized gases. The collector andseal assembly 130 includes an annular polymeric seal 140 and a currentcollector 132. The current collector and seal assembly 130 of the fourthembodiment does not require an inner cover as used in the collector andseal assemblies of the first, second, and third embodiments describedabove.

The current collector 132 includes a lower cylindrical shaft 134, anenlarged diameter step 139, a reduced diameter cylindrical shaft 137,and an enlarged head 136 at the upper end. The lower shaft 134 ofcurrent collector 132 extends into and contacts anode 26. The reduceddiameter shaft 137 is located between the enlarged diameter step 139 andenlarged head 136, and preferably has a diameter less than the diameterof the lower shaft 134. The upper surface of enlarged head 136 may bewelded to, or in pressure contact with, outer negative cover 150.

The annular seal 140 includes a central hub 142 having an innerupstanding wall 144 defining a central opening for receiving the currentcollector 132. The outer peripheral portion 145 of seal 140 forms asealed closure against the can 12 and provides dielectric isolationbetween steel can 12 and outer negative cover 150. It should beappreciated that the open end 16 of the can 12, seal 140, and outercover 150 are crimped so as to compress the seal 140 and provide asealed closure. The current collector 132 is interference fit within theopening formed by inner upstanding wall 144 of seal 140. The innerupstanding wall 144 of seal 140 is compressed against current collector132 and sealingly engages the current collector 132 when in a sealed(non-vented) position as shown in FIG. 8.

Referring to FIG. 9, the electrochemical cell 110 is shown with thecollector and seal assembly 130 in a vented position. When the internalpressure within the sealed volume of electrochemical cell 110 exceeds apredetermined pressure threshold, relative to the atmospheric pressure,the central hub 142 of seal 140 is forced upward due to the differentialpressure applied to the seal 140. When the pressure differential exceedsthe pressure threshold, hub 142 is forced over the enlarged diameterstep 139 to a position above step 139 to provide a pressure reliefpassage 148 between seal 140 and current collector 132. When thisoccurs, the entire hub 142 is forced upward relative to the currentcollector 132 which remains substantially fixed in place. It should beappreciated that the current collector 132 may move upward a smalldistance, however, it is a relatively small distance compared to themovement of the entire hub 142 of seal 140. By providing the reduceddiameter section 137, the pressure relief path 148 is provided withoutallowing resealing between reduced diameter section 137 and seal 140.Outer cover 150 includes one or more vent openings 152 to vent pressurebuild-up released from within cell 110 to the outside atmosphere.

Once the pressure differential has decreased to a lower pressure, thehub 142 of seal 140 may slide downwardly (retract) back into sealingengagement on the upper side of the enlarged diameter step 139 as shownin FIG. 10. Central hub 142 of seal 140 has a shaped surface indentation(bevel) 141 provided in the lower section of upstanding wall 144 whichsubstantially conforms to the shape of the upper surface of enlargeddiameter step 139. Upon retracting downward, the seal 140 may againsealingly engage current collector 132 to prevent further discharge ofgases and other material. It should be appreciated that upon thepressure differential increasing, additional venting of pressurizedgases may occur.

With particular reference to FIG. 11, the annular polymeric seal 140 isshown having a plurality of channels 160 formed in the upper surface. Itshould be appreciated that by employing one or more standoff members,such as channels 160, in the upper surface of seal 140, the channels 160provide a vent path to prevent resealing of seal 140 with currentcollector 132 when in the vent position. It should also be appreciatedthat as an alternative to channels, other standoff members, such as ribsor other surface protrusions, may be provided either on the uppersurface of seal 140 or on the surface of current collector 130 toprevent resealing during the venting operation. Examples ofanti-resealing assemblies are disclosed in U.S. application Ser. No.09/300,413, filed Apr. 27, 1999, entitled “ELECTROCHEMICAL CELL HAVINGLOW PROFILE SEAL ASSEMBLY WITH ANTI-RESEALING VENT,” which is herebyincorporated by reference.

Referring to FIGS. 12 and 13, an electrochemical cell 110′ isillustrated having a collector and seal assembly 130′ according to afifth embodiment of the present invention. The electrochemical cell 110likewise includes a steel can 12, label 20, cathode 22, separator 24,anode 26, and other components as discussed above. The collector andseal assembly 130′ of the fifth embodiment includes a current collector132′ having a lower shaft 134, an enlarged diameter step 139, and aplurality of longitudinal flutes (i.e., channels) 162 extending from theenlarged diameter step 139 upward toward the enlarged head 136. Thecurrent collector 132′ is likewise connected to the outer negative cover150. The plurality of flutes 162 provide pressure relief passages 148for releasing pressurized gases from the internal volume of the cell110′ in a controlled operation. In the non-vented position, shown inFIG. 12, the hub 142 of seal 140 provides sealing engagement betweenupstanding walls 144 and each of shaft 134 and step 139 of currentcollector 132′. The shaft 134 of current collector 132′ is interferencefit within the opening formed by the inner walls of hub 142 of seal 140.When the internal pressure within the sealed volume of cell 110′increases beyond a predetermined pressure threshold, the central hub 142slides upward along current collector 132′ until one or more pressurerelief passages 148 are provided through flutes 162 to release the highpressure gases from within the sealed volume, as shown in FIG. 13. Itshould be appreciated that the current collector 132′ remainssubstantially fixed, relative to the movement of the entire hub 142 ofseal 140, as discussed above. By providing a plurality of flutes 162 toserve as the pressure relief passages, a controlled low pressure releaseof gases may be achieved according to this embodiment.

The seal member 140 is made of a polymeric material, such as Noryl®Extend which is commercially available from General Electric Company ofSelkirk, N.Y. Noryl® Extend is a polypropylene matrix havingpolyethylene therein, which acts as a polymer stiffener. Noryl® Extendprovides low moisture absorption, will not hydrolyze in the presence ofKOH, and has very low stress relaxation. These characteristics allow theseal design of the present invention to be feasible, whereas use of amaterial such as nylon for the seal 140 of the present invention wouldrequire the use of a support. This is due to nylon cracking in thepresence of KOH coupled with stress on the seal (in the hoop direction)due to the nail vent design.

It should be appreciated that, while Noryl® Extend is a preferredmaterial for seal 140 that resists cracking, particularly in the centralhub, other seal materials could be used. For example, the seal members40 and 140 may include nylon, such as Zytel® 101F, which is commerciallyavailable from E.I. duPont deNemours and Co. Inc. Seal members 40 and140 can be integrally formed using a conventional injection moldingprocess. In addition, the bottom surface of seal members 40 and 140 maybe coated with a layer of asphalt (not shown) or other suitable materialto prevent chemical degradation of the seal member due to the presenceof electrolyte.

While the various embodiments described herein provide a pressure reliefpassage achieved by relative axial movement between a collector and aseal, it should be appreciated that other vent passages may be provided.For example, the relative movement between the seal and collector may bedesigned to cause the seal hub to split open, thereby further creating apressure relief passage through the split opening.

Accordingly, the present invention advantageously provides collector andseal assemblies for sealing the open end of an electrochemical cell andrealizing a controlled venting operation to vent high pressure gases,particularly when the cell is subjected to an abusive condition. Thecollector and seal assemblies of the present invention each offer asimplified seal design in a low profile assembly which results ingreater volume available for active battery components. The seals of thepresent invention are easy to mold, since no conventional thin sectionsare required for the vent diaphragm. In addition, a wide range of ventpressures is achievable by adjusting the nail step diameter in itsrelation to the seal hub inside diameter, seal hub outside diameter, andnail diameter below the enlarged diameter step. The venting rate caneasily be adjusted with the collector and seal assemblies of the presentapplication. Generally, the pressurized gases in the cell will escapefaster if the diameter difference between the vent region of the nailand seal is made greater, and if the vent channel cross section area ontop of the seal is increased. Likewise, the seal can be designed to ventslower to create less release spray if the diameter clearance isdecreased or the vent channel is decreased. By providing the seal suchthat it can flex back to a non-vent position, reduced or preventedleakage of electrolyte after the seal has vented can be achieved.Further, it should be appreciated that the collector and seal assembliesof the present invention employ fewer parts and less volume thanconventional seal assemblies.

While the collector and seal assemblies have been described herein inconnection with a cylindrical bobbin-type electrochemical cell, itshould be appreciated that the invention concepts are likewiseapplicable to various other cell configurations including jelly rollcells, prismatic cells, cells employing multiple anodes and multiplecurrent collectors and cells in which the cans and current collectorsare electrically connected to the negative and positive electrodes,respectively. Additionally, it should also be appreciated that thecollector and seal assemblies described herein may be sealed closedagainst the steel can using various different can closures.

It will be understood by those who practice the invention and thoseskilled in the art, that various modifications and improvements may bemade to the invention without departing from the spirit of the disclosedconcepts. The scope of protection afforded is to be determined by theclaims and by the breadth of interpretation allowed by law.

1. An electrochemical cell comprising a container having a bottom endand an open top end; a positive electrode disposed in the container, anegative electrode disposed in the container; a seal member disposed inthe open top end of the container for closing the open top end of thecontainer, the seal member having an opening defined by a wall; and acurrent collector having a shaft extending through the opening in theseal member and contacting one of the positive and negative electrodes;wherein: the current collector shaft has a surface adjacent to the sealmember wall; the seal member wall has a surface adjacent to the currentcollector shaft; a portion of the surface of the current collector shaftis in sealing contact with at least a portion of the seal member wallwhen in a sealed position; and at least one of the current collectorshaft and the seal member wall is axially moveable from the sealedposition to a vent position upon experiencing a predetermined pressure,thereby breaking at least a portion of the sealing contact to provide apressure relief passage for venting pressurized gases between thesurfaces of the current collector shaft and the seal member wall when inthe vent position.
 2. The electrochemical cell as defined in claim 1,wherein the current collector shaft comprises a round surface and theopening in the seal member wall is round.
 3. The electrochemical cell asdefined in claim 1, wherein the current collector shaft is moveable fromthe sealed position to the vent position.
 4. The electrochemical cell asdefined in claim 3, wherein the surface of the shaft comprises a firstwidth and a second width, at least a portion of the first width is aboveand larger than the second width and makes sealing contact with at leasta portion of the surface of the seal member wall when in the sealedposition, and the shaft is moveable upward to the vent position toprovide a pressure relief passage between at least a portion of thesecond width of the shaft and at least a portion of the surface of theseal member wall.
 5. The electrochemical cell as defined in claim 4,wherein the second width of the shaft comprises one or more flutes inthe surface of the shaft.
 6. The electrochemical cell as defined inclaim 3, wherein the sealing contact between the current collector shaftand the seal member wall comprises a compressed area in the seal memberwall.
 7. The electrochemical cell as defined in claim 3, wherein aportion of the seal member wall extends inward above a portion of thecurrent collector shaft.
 8. The electrochemical cell as defined in claim3, wherein the cell comprises a terminal cover electrically coupled tothe current collector.
 9. The electrochemical cell as defined in claim8, wherein the current collector shaft is biased downward by a springelectrically coupling the top of the shaft and the terminal cover, andthe spring is compressible to allow upward movement of the shaft to thevent position when the predetermined pressure is reached.
 10. Theelectrochemical cell as defined in claim 9, wherein the spring is a coilspring.
 11. The electrochemical cell as defined in claim 9, wherein thespring is a bowl-shaped disk.
 12. The electrochemical cell as defined inclaim 3, wherein the current collector shaft, after moving to the ventposition, is moveable into sealing contact with the seal memberfollowing initial venting.
 13. The electrochemical cell as defined inclaim 1, wherein the seal member wall is moveable to the vent position.14. The electrochemical cell as defined in claim 13, wherein the surfaceof the shaft comprises a first width and a second width below at least aportion of the first width, the sealing contact between the shaft andthe seal member wall in the sealed position is between at least aportion of the second width of the shaft and at least a portion of theseal member wall, and the seal member is moveable upward to the ventposition to provide a pressure relief passage between at least a portionof the first width of the shaft and at least a portion of the sealmember wall.
 15. The electrochemical cell as defined in claim 14,wherein the first width of the shaft is smaller than the second width.16. The electrochemical cell as defined in claim 15, wherein the shaftcomprises a third width that is larger than the second width anddisposed is between the first and second widths, and the seal memberwall must move over the third width to the vent position.
 17. Theelectrochemical cell as defined in claim 14, wherein the first width ofthe shaft is larger than the second width, the first width can restrainupward movement of the seal member wall until the predetermined pressureis reached, and the one or more flutes in the surface of the shaftprovide a pressure relief passage between the surface of the shaft andthe surface of the seal member wall when the seal member wall movesupward to the vent position.
 18. The electrochemical cell as defined inclaim 13, wherein a top surface of the seal member comprises a vent pathto prevent resealing of the current collector and seal member when inthe vent position.
 19. The electrochemical cell as defined in claim 13,wherein the sealing contact between the current collector shaft and theseal member wall comprises a compressed area in the seal member wall.20. The electrochemical cell as defined in claim 3, wherein the cellcomprises a terminal cover electrically coupled to the currentcollector.
 21. The electrochemical cell as defined in claim 3, whereinthe seal member wall, after moving to the vent position, is moveableinto sealing contact with the current collector shaft following initialventing.
 22. An electrochemical cell comprising a container having abottom end and an open top end; a positive electrode disposed in thecontainer, a negative electrode disposed in the container; a seal memberdisposed in the open top end of the container for closing the open topend of the container, the seal member having an opening defined by awall; a current collector having a shaft extending through the openingin the seal member and contacting one of the positive and negativeelectrodes; and an outer cover disposed over the seal member; wherein:the current collector shaft has a surface adjacent to the seal memberwall; the seal member wall has a surface adjacent to the currentcollector shaft; a portion of the surface of the current collector shaftis in sealing contact with at least a portion of the seal member wallwhen in a sealed position; the current collector shaft is biaseddownward in the sealed position; and the current collector shaft isaxially moveable from the sealed position to a vent position uponexperiencing a predetermined pressure, thereby compressing the springand breaking at least a portion of the sealing contact to provide apressure relief passage for venting pressurized gases between thesurfaces of the current collector shaft and the seal member wall when inthe vent position.
 23. The electrochemical cell as defined in claim 22,wherein the current collector shaft comprises a round surface and theopening in the seal member is round.
 24. The electrochemical cell asdefined in claim 23, wherein the surface of the shaft comprises a firstwidth and a second width disposed below at least a portion of the firstwidth, at least a portion of the first width of the shaft makes sealingcontact with at least a portion of the surface of the seal member wallwhen in the sealed position, and the shaft is moveable to the ventposition to provide a pressure relief passage between at least a portionof the second width of the shaft and at least a portion of the surfaceof the seal member wall.
 25. The electrochemical cell as defined inclaim 24, wherein the second width of the shaft comprises one or moreflutes in the surface of the shaft.
 26. An electrochemical cellcomprising a container having a bottom end and an open top end; apositive electrode disposed in the container, a negative electrodedisposed in the container; a seal member disposed in the open top end ofthe container for closing the open top end of the container, the sealmember having an opening defined by a wall; a current collector having ashaft extending through the opening in the seal member and contactingone of the positive and negative electrodes; and an outer cover disposedover the seal member; wherein: the current collector shaft has a surfaceadjacent to the seal member wall; the seal member wall has a surfaceadjacent to the current collector shaft; a portion of the surface of thecurrent collector shaft is in sealing contact with at least a portion ofthe seal member wall when in a sealed position; and the seal member wallis axially moveable from the sealed position to a vent position uponexperiencing a predetermined pressure, thereby breaking at least aportion of the sealing contact to provide a pressure relief passage forventing pressurized gases between the surfaces of the current collectorshaft and the seal member wall when in the vent position.
 27. Theelectrochemical cell as defined in claim 26, wherein the currentcollector shaft comprises a round surface and the opening in the sealmember is round.
 28. The electrochemical cell as defined in claim 26,wherein the surface of the shaft comprises a first width and a secondwidth below at least a portion of the first width, the sealing contactbetween the shaft and the seal member wall in the sealed position isbetween at least a portion of the second width of the shaft and at leasta portion of the seal member wall, and the seal member is moveableupward to the vent position to provide a pressure relief passage betweenat least a portion of the surface of the shaft and at least a portion ofthe surface of the seal member wall.
 29. The electrochemical cell asdefined in claim 28, wherein the first width of the shaft is smallerthan the second width.
 30. The electrochemical cell as defined in claim29, wherein the shaft comprises a third width that is larger than thesecond width and disposed is between the first and second widths, andthe seal member wall must move over the third width to the ventposition.
 31. The electrochemical cell as defined in claim 28, whereinthe first width of the shaft is larger than the second width, the firstwidth can restrain upward movement of the seal member wall until thepredetermined pressure is reached, and one or more flutes in the surfaceof the shaft provide a pressure relief passage between the surface ofthe shaft and the surface of the seal member wall when the seal memberwall moves upward to the vent position.